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In English, when joining two clauses, we frequently omit certain words to avoid redundancy and (to) increase clarity. How far can you go with this rule? I tried to come up with a few examples....please let me know if any are grammatically incorrect.

(1) past + conjunction + past

John had pizza for lunch. + but + John had sushi for dinner.

John had pizza for lunch but he had sushi for dinner.

John had pizza for lunch but had sushi for dinner.

John had pizza for lunch but sushi for dinner.

(2) present + past

John is a good person. + but + John had temper problems in the past.

John is a good person, but he had temper problems in the past.

John is a good person, but had temper problems in the past. --incorrect?

(3) present perfect continuous + present

John has been swimming for hours. + but + John still shows no sign of fatigue.

John has been swimming for hours, but he still shows no sign of fatigue.

John has been swimming for hours, but still shows no sign of fatigue. --incorrect?

Thank you!
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RIP(1) John had pizza for lunch but sushi for dinner.
(2) John is a good person, but had temper problems in the past.
(3) John has been swimming for hours, but still shows no sign of fatigue.
I think they are all correct.

paco
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Fine also, Rip.
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Hi, thanks for your input. Another thing popped up in my mind: what about mixing active and passive voices?

Ex: The components cover the top surface of device1. + The components are attached to device 2.

The components cover the top surface of device1 and are attached to device2? --correct?

Thanks!
You can write even this:
The components are covering the device #1 and attached to the device #2.

I had a similar problem myself and asked it here. The problem is not of grammar but of writing style. A good writing is such that the readers can easily take the sense. If you make ellipsis too much, you readers will get troubled to take the sense. An example of bad ellipsis is like this:
[1] I have been in the States and I have to visit my old friends there this autumn.
[2] I have been in the States and have to visit my old friends there this autumn.[OK]
[3] I have been in the States and to visit my old friends there this autumn.[??]
Is the sentence [3] easy to take the sense for you?

paco
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Thanks Paco, I appreciate all your inputs.

So mixing two clauses, one with an active verb and one with a passive verb, is ok?

What about something like this within a nonrestrictive clause?

ex: Device1, which is attached to device2 and supplies current to device3, ....

(device1, which is attached to device2,... + device1, which supplies current to device3,....) passive + active
 Mister Micawber's reply was promoted to an answer.